A commercially available folding knife is typically composed of a handle and a blade. One end of the blade is pivotally connected to one end of the handle so that the blade can be rotated about a pivot either out of the handle or into the handle for storage. When it is desired to use the folding knife, the handle is held in one hand, and the blade is pulled with the other hand in order to rotate the blade out of the handle. As the blade cannot be rotated out of the handle without using both hands, a user may have problem opening the knife in a special or emergency situation where only one hand is available. For example, a diver having one hand caught in a fish net may find it difficult to cut off the net immediately with the folding knife, which puts the diver's life in danger. To solve the problem, a folding knife with an elastic element was designed, allowing the user to rotate the blade out of the handle single-handedly, as explained in more detail in the following paragraphs.
Referring to FIG. 1A and FIG. 1B, the folding knife 1 includes a handle 11, a blade 12, an elastic element 13, and a pushing element 14. The blade 12, which has one end pivotally provided at one end of the handle 11, can be rotated about an axis defined by the pivotally connected portions of the blade 12 and the handle 11. More specifically, the blade 12 can be rotated out of the handle 11 for use (e.g., for cutting an object) or into the handle 11 for storage. In the latter case, the folding knife 1 is also reduced in volume and can be carried around conveniently, without fear that the blade 12 will cause human injury or damage. The elastic element 13 has one end fixedly provided in, and adjacent to, the other end of the handle 11. The other end (hereinafter referred to as the second end) of the elastic element 13 extends to a position adjacent to where the handle 11 and the blade 12 are pivotally connected. When the blade 12 is completely received in the handle 11 (as shown in FIG. 1A), the second end of the elastic element 13 abuts against the blade 12 at a position adjacent to where the handle 11 and the blade 12 are pivotally connected (e.g., against a post 121 provided on the blade 12, as shown in FIG. 1A and FIG. 1B), thereby generating a torque tending to rotate the blade 12 further into the handle 11 (as indicated by the arrow in FIG. 1A); as a result, the blade 12 is firmly received in the handle 11. Once the blade 12 is rotated out of the handle 11 to a predetermined angle, the elastic element 13 generates a torque tending to rotate the blade 12 further out of the handle 11 (as indicated by the arrow in FIG. 1B) such that the blade 12 spins out of the handle 11 automatically.
As shown in FIG. 1A and FIG. 1B, the pushing element 14 is pivotally connected to the handle 11 and the blade 12. As shown in FIG. 1A, the pushing element 14 is a plate-shaped element and has one end extending out of the handle 11 and protrudingly provided with a pushing portion 141 to be pushed by the user. Another end of the pushing element 14 is provided with a pressing portion 142. When the blade 12 is completely received in the handle 11, as shown in FIG. 1A, the pressing portion 142 abuts against the blade 12. If the user pushes the pushing portion 141 now, the pushing element 14 will be rotated and drive the pressing portion 142 to push the blade 12. Consequently, the blade 12 is rotated out of the handle 11 to the predetermined angle, and thanks to the torque generated by the elastic element 13 to rotate the blade 12 further out of the handle 11, the blade 12 spins out of the handle 11 automatically, as shown in FIG. 1B. Therefore, the user only has to hold the handle 11 firmly in one hand and push the pushing portion 141 gently with a finger, and the blade 12 will spring out of the handle 11 rapidly and smoothly, allowing the user to deal with the emergency at hand. As such, the convenience and safety of use of the folding knife 1 are effectively enhanced.
While the folding knife described above can be operated with only one hand, which is truly convenient, its operation can be extremely dangerous to children due to the fact that the pushing portion of the pushing element protrudes conspicuously from the handle. More specifically, anyone who has overcome the force applied by the elastic element to the blade (i.e., the post) can turn the pushing element and cause the blade to spin out of the handle. Hence, it has been an important issue in the folding knife industry to design a folding knife structure which retains the pushing element but somehow increases the difficulty with which the pushing element can be pushed, thereby preventing the blade from being easily rotated out of the handle by children.